At the top of your PowerPoint presentation, there are a small handful of tool buttons that you can click on. Just to the right of the + and - Zoom buttons, there is a diagonal double-pointed arrow. This will enlarge the PowerPoint to fill most of your screen ... though there still may be some white borders on each side. You can press the "Esc" key on your keyboard to return to your normal course view.
Regarding the white column where the PowerPoint isn't displaying anything. This is actually a setting that is controlled by your school's Canvas administrator(s). It is a Feature Option called "New User Tutorial". My guess is that your Canvas admin(s) do not have this setting enabled. I know this setting sounds unrelated, but if it is enabled, then you will see that a lot of your content in your Canvas courses will fill out more to the edge of the screen rather than showing that white space. If you had a conversation with your school's Canvas admin(s), maybe they would be willing to flip this switch "on". But, keep in mind that turning "New User Tutorial" on would enable it for everyone at your school...not just you and the others in your class...as it affects every class that is in Canvas. This is the admin Guide that you could show your Canvas admin:
How do I manage new features for an account? - Instructure Community (canvaslms.com)
I hope this will help a bit. Sing out if you have any other questions about this...thanks!